This invention is directed to a single connector having terminal selections for a printer used for word processing or other microcomputer output. Two such connectors are known in the prior art, both known as incorporated in commercially sold printers.
The Texas Instruments Model 855 printer is understood to have a single connector with contacts carrying most of the signals used in accordance with this invention. The serial interface contacts differ from those of this invention in not having a Request to Send signal contact and in not having a Clear to Send signal contact and in having a Secondary Request to Send signal contact, a contact not necessarily employed in this invention. This prior art also has some differences in its parallel and other signals. These prior art signals are shown in detail in the body of this specification.
The Diablo Models 630 API/API ECS Communications Terminals have a connector of 50 contacts providing two parallel modes of communication and one serial mode of communication. These serial connectors do not include Request to Send and Clear to Send, contacts which are employed in the subject invention. (It does have a constant 12 volt signal on its pin 23 which is interpreted as a Request to Send signal.) This prior art also has some differences in its parallel and other signals. These prior art signals are shown in detail in the body of this specification.
The Electronic Industries Association (EIA) standard for the RS-232-C serial interface recognizes limited sets of signals, denominated Interface Types, for different communication systems. The set of serial signals in accordance with this invention is very similar to the Type D interface, a duplex interface, but the Type D interface, in addition to requiring all of the serial signals employed in the preferred embodiment of this invention except Data Terminal Ready, requires an additional signal, the Received Line Signal Detector. The Type D interface also specifies Data Terminal Ready and Ring Detector as additional signals for Switched Service. The Type x interface of the EIA standard requires Signal Ground with all other signals being specified for the specific purpose. The set of serial signals in accordance with this invention therefore may be considered a Type x interface under the EIA standard.
An alternative to the use of separate contacts for each mode of communication as employed with this invention is to physically switch the contacts between circuits for parallel communication and circuits for serial communication, so that all of the contacts can be used in both the modes of communication. This is unacceptably expensive, however, and poses potential problems in space availability and mechanical reliability. In accordance with this invention circuits specific for the purpose of each contact are permanently connected to the contact and all are powered to an operating status when the printer is powered for operation. Thus, typically, a parallel contact may be brought to zero or plus +5 volts and a serial contact is brought to between -3 volts to -15 volts or to between +3 volts to +15 volts. Since the circuit levels are different, a contact having circuits to receive for example, parallel signals ordinarily would not respond to transmitted serial signals, which vary across a much wider range than the parallel signals.